Introduction

This tutorial is intented for people who are using Debian, and want to check out or test some idea on existing KDE code without much hassle.

This tutorial shows a way of easily downloading and compiling and running the KDE software that is used on your Debian system.

Getting started

First you need to add the source repositories to your installation. This is normally done by editing /etc/apt/sources.list as user root and adding a line starting with deb-src:

kdesudo kwrite /etc/apt/sources.list
</code>
The easy way is to copy your existing <tt>deb</tt> line onto a new line, and change <tt>deb</tt> to <tt>deb-src</tt>:
<code bash n>
deb http://ftp.belnet.be/debian testing main contrib non-free
deb-src http://ftp.belnet.be/debian testing main contrib non-free #almost a copy of line 1</code>
In most(all?) of the cases this will work.
Then you must let this change know to the package manager, so doas root:
<syntaxhighlight lang="bash">aptitude update</code>
== Setting up the dependencies ==
Now you want to be able to build a certain package, and in this example we will build the kcontrol configuration modules(aka KCM modules) and the application containing them called systemsettings. Let's say we want to see if we can maybe fix some bug in the Display configuration module, which is called <tt>randr</tt> actually. In debian the package is <tt>systemsettings</tt>, so first we will get the build dependencies of that package, so do as root:
<syntaxhighlight lang="bash">aptitude build-dep systemsettings</code>
This will download and install all needed dependencies which are some build tools and otherwise mostly packages with <tt>-dev</tt> at the end of them, which are in most cases a bunch of header files.
== Getting the source ==
As a regular user, create a new directory, and fetch the sources for the package:
<syntaxhighlight lang="bash">
mkdir ~/kde4devel
cd ~/kde4devel
apt-get source systemsettings
</code>
This downloads the source and applies all the debian patches for you. In this case, it downloads <tt>kdebase-workspace</tt> because the systemsettings code is only a small part of the kdebase-workspace package. Now go into the newly extracted directory. This is {{Path|kdebase-workspace-4.3.2}} in my case.
<syntaxhighlight lang="bash">
cd kdebase-workspace-4.3.2
</code>
== Building the source ==
Now we go into the source directory, and let <tt>cmake</tt> generate the Makefiles, which are then used by the <tt>make</tt> command to build the code. This is done like this:
<syntaxhighlight lang="bash">
cmake . # don't forget the extra space+point!</code>
Later we'll have to install the built files, you probably don't want to do this as root. So it is better to call <tt>cmake</tt> like this:
<syntaxhighlight lang="bash">
cmake -DCMAKE_INSTALL_PREFIX=$HOME/kde4devel/root .
</code><tt>cmake</tt> supports a nice Qt GUI to configure your build process. If you have the package <tt>cmake-qt-gui</tt> installed, you can replace <tt>cmake</tt> with <tt>cmake-gui</tt>. More information on <tt>cmake</tt> is available in the [http://techbase.kde.org/Development/Tutorials/CMake CMake Tutorial].
With <tt>cmake-gui</tt> it is easy to select only the components starting with <tt>BUILD_</tt> you want. In my case it was rather the components I'm sure of that I didn't want :). So I ended up with only <tt>BUILD_kcontrol</tt> and <tt>systemsettings</tt> and didn't touch any of the other settings below. Then click on the <tt>Configure</tt> button and, if successful, then on the <tt>Generate</tt> button. Close the program now.
Now we have makefiles that will only build what we chose to build in the <tt>cmake-gui</tt> program. So now you can execute the <tt>make</tt> command to start:
<syntaxhighlight lang="bash">
make
</code>
Now it is building!
== Changing the source ==
We will now go to the directory of the randr module we want to develop on:
<syntaxhighlight lang="bash">
cd kcontrol/randr
</code>
Edit some file, and then rebuild simply by running <tt>make</tt> again in this directory:
<syntaxhighlight lang="bash">
make
</code>
The module is now being rebuilt.
Likewise we can change something in a source file in the <tt>systemsettings</tt> source directory, and rebuild it using <tt>make</tt>
<syntaxhighlight lang="bash">
cd ~/kde4devel/kdebase-workspace-4.3.2/systemsettings
make
</code>
To have a full rebuild of the code, first do <tt>make clean</tt> before the <tt>make</tt> command.
== Running the program ==
This may be somewhat difficult, but we start easy ;)
You go into the {{Path|systemsettings/app}} directory, and there start that self-compiled code like this:
<syntaxhighlight lang="bash">
cd ~/kde4devel/kdebase-workspace-4.3.2/systemsettings/app
./systemsettings
</code>
This will indeed run your new code. But it is better to first install it into your {{path|~/kde4devel/root}} directory so everything is setup correctly in a certain hierarchy, because the systemsettings program might need to find or access certain files to function properly. You do this with the simple command <tt>make install</tt> in the main directory of the application or module you just built:
<syntaxhighlight lang="bash">
cd ~/kde4devel/kdebase-workspace-4.3.2/systemsettings
make install
cd ~/kde4devel/kdebase-workspace-4.3.2/kcontrol/randr
make install
</code>
However! '''Here is the difficult part...''' We already have a systemsettings program installed: the one installed by the Debian system in {{path|/usr/bin/systemsettings}}. So you will now find that we have a second one of our own in {{path|~/kde4devel/root/bin/systemsettings}}.
{{note|'''So remember this''': Debian installs everything under {{path|/usr}} and your programs end up under {{path|~/kde4devel/root/local}} }}
The <tt>make install</tt> command copied more than only the executable file! It also copied e.g. {{path|~/kde4devel/root/lib/kde4/kcm_randr.so}}. So when we start our "local" systemsettings program, we want to make sure it first finds the files it installed under {{path|~/kde4devel/root}}, and not first the files installed by Debian under {{path|/usr}}.
We need to tell our current console session the additional KDE path where it needs to look for services and libraries and programs. This is done by filling in the <tt>KDEDIRS</tt> environment variable like this:
<syntaxhighlight lang="bash">
export KDEDIRS=$HOME/kde4devel/root
</code>
Now when we start the systemsettings module in this console session it will find the kcontrol configuration module located in {{path|~/kde4devel/root/lib/kde4/kcm_randr.so}} before the one in {{path|~/kde4devel/root/kde4/kcm_randr.so}}:
<syntaxhighlight lang="bash">
cd ~/kde4devel/root
./systemsettings
</code>
And you will now see your own compiled code in action!
== Conclusion ==
Now you have completed compiling and running your own compiled code, you are ready to check out the other tutorials here and gain some deeper insights!